Pre-stressed Concrete

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In this type of concrete initial compression is given before applying to the external loads thus loads from the external loads can be counteracted in the appropriate way.

We all know that concrete is good at compression but weak in tension so when it is subjected to external loads it tension zone occurred in the lower part of concrete hence cracks occur and to prevent this problem we are using the steel reinforcement at the bottom section and this is our traditional method of RC structure but what happen when we are constructing mega structures of larger beam spans? By using this traditional way to the larger beam span in bridge construction where we need to give larger depth there is no space for ships to pass and then this new concept has come.

It is now commonly used for floor beams, piles and railways sleepers, as well as structures such as bridges, water tanks, roofs and runways. Generally, prestressed concrete is not necessary for columns and walls, however, it can be used economically for tall columns and high retaining walls with high bending stresses.

Methods of Pre-stressing

Internal Pre-stressing

In this system, a pre-stressing force is applied to the high tensile steel, i.e., the steel reinforcement. It induces internal compressive stresses in concrete. This most commonly used method because of the easy and accurate application.

Internal pre-stressing can be done by two different methods :

Pre-tensioning

Post-tensioning

External Pre-stressing

In this method, the pre-stressing is done by adjusting the external reactions. Simply supported beam is pre-stressed externally by jacks. The externally pre-stressing system requires very much accuracy in planning and application. This is not commonly used method.

Pre-Tensioning

In Pre-tensioning, the steel tendons are tensioned before the concrete is cast. The tendons are temporarily anchored against some abutments and then cut or released after the concrete has been placed and hardened. The pre-stressing force is transferred to this concrete by the bond along the length of the tendon. Pre-tensioning is generally done in pre-casting plants in permanent beds, which are used to produce Pre-tensioned precast concrete elements for the building industry.

Post-Tensioning

In Post-tensioning, the steel tendons are tensioned after the concrete has been cast and hardened. Post-tensioning is performed by two main operations: tensioning the steel wires or strands by hydraulic jacks that stretch the strands while bearing against the ends of the member and then replacing the jacks by permanent anchorages that bear on the member and maintain the steel strands in tension. In the post-tensioning process, the steel tendons are placed in the formwork before the concrete is cast, and the tendons are prevented from bonding to the concrete by waterproof paper wrapping or a metal duct (sheath). 

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Blog Written by
Shruti Doshi
Technical Officer – Sanghi Cement & Blogger
shrutidoshi.1492@gmail.com


Blog Managed by
Nirav Pandya
Digital Marketing Officer – Sanghi Cement
nirav.pandya@sanghicement.com

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